The invention relates to ultrasound imaging. More specifically, the invention relates to automatically adjusting the gain of received ultrasound signals when performing ultrasound imaging.
Ultrasound is used to image human bodies to diagnose various medical conditions of, for example, a fetus, the heart, liver, kidney and other organs. Ultrasound is transmitted by an ultrasound transducer through the skin to tissues in the human body. The ultrasound is scattered by ultrasound scatterers and is received by the ultrasound transducer. The received ultrasound is converted to an electrical signal by the ultrasound transducer and is processed to create an image of the tissues.
Ultrasound is attenuated through the human tissues at a rate of approximately 0.5 dB/MHz/cm. The intensity of the ultrasonic beam decreases as it penetrates the tissue. Therefore, two identical targets at different depths will produce different echoes with the echo produced by the closer target being larger than the other. This problem may be circumvented by using time-gain compensation (TGC) in which the gain of the received signal amplifier is increased as a function depth (time) to compensate for the loss in energy due to attenuation. Various forms of time-gain compensation have been used. In modern scanners, TGC shape may be conveniently adjusted to optimize the image or the application.
Conventional ultrasound imaging systems are usually equipped with TGC to compensate for this type of attenuation. However, most systems use either a fixed TGC or an operator adjustable TGC. If the received ultrasound signal is not compensated for, the resulting ultrasound image would be brighter at a shallow depth and darker at a larger depth resulting in a non-uniform image.
Fixed TGC uses a predetermined attenuation curve for all imaging which is not optimal since attenuation in patient's bodies varies from one patient to another. Adjustable TGC is controlled by an operator by sliding potentiometers on the control console. Typical ultrasound systems include several potentiometers for the operator to adjust to create an attenuation compensation curve that provides a uniform image. The operator needs to set the TGC potentiometers for every patient and for every location of the human body to image. If the TGC settings are set inaccurately, diagnostic quality may suffer.
Operator adjustable TGC is time consuming, and may adversely affect a patient's diagnosis. There exists a need to automatically adjust TGC using signals from the patient for each ultrasound image.